Lecture 49
Light and Color
Ozgur Unal
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How many colors are there in the Philippine flag?
Why do some objects appear red, while others look green or
yellow?
How about white and black?
When a red apple is struck by white light, it reflects red light
back to your eyes and absorbs all of the other colors.
White objects reflect all colors.
Black objects do not reflect any color, they absorb all colors.
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A filter is a transparent material that transmits one or more
colors of light but absorbs all others.
The color of a filter is the color of the light it transmits.
Check out Figure 25.
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Light and the eye:
In a healthy eye, light enters the
eye through the cornea.
Retina is made up of two types
of cells that absorb light: cone cells
and rod cells.
Cone cells need bright light to
generate nerve impulses.
Cones do not operate in dim
light  even brightly colored objects
might look gray or black in dim light.
3 types of cones: red cones, green
cones and blue cones
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Rod cells are sensitive to
dim light and enables you
to see at night.
Rod cells are mostly located
around cone cells.
Humans have many more rod cells than cone cells  this
enables us to see at night.
How about nocturnal animals?
Infer the number of rods in the
eyes of these animals.
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Can you read the number below?
The most common form of color blindness makes it difficult
to distinguish between red and green.
8% of men and 1.5% women are color blind.
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The colors are a result of mixtures of pigments.
Blue + Yellow  Green
A pigment is a colored material that is used to change the
color of other substances.
The color of a pigment results from the different
wavelengths of light that the pigment reflects.
Mixing Colored Lights:
All colors can be made by mixing
three colors of light: blue, red and
green  primary colors
Mixing primary colors in equal
amounts gives white.
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Paint Pigments:
If you mix equal amounts of red, blue and green paint do
you get white?
Paints are made with pigments.
Pigments produce color as a result of the wavelengths of
light they reflect.
Mixing Pigments:
You can make any pigment color
by mixing three primary pigments:
magenta (bluish red), cyan
(greenish blue) and yellow.
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